How to Downgrade macOS Big Sur to macOS Catalina without Losing Data

By Connie | Posted to Mac Data Recovery Tips, updated on February 19th, 2021 | User rating:

You may have the question: "Can I downgrade macOS Big Sur to Catalina?". The answer is definitely yes.

Upgrading to the latest macOS Big Sur requires you to adapt its new features and redesigned look. Moreover, you also have to accept the macOS 11 Big Sur updates issues like software incompatibility.

If you regretted upgrading macOS Big Sur because of its massive changes and frustrating issues, downgrade to macOS Catalina will eliminate your annoyance. Note that if it is an M1 Mac, you can't revert from the macOS Big Sur to macOS Catalina.

How to downgrade macOS Big Sur to macOS Catalina

In this post, you can get the stepwise methods for downgrading macOS.

Preparations before downgrading macOS Big Sur to Catalina

Downgrading macOS will cause all data on your Mac lost. If you only need a few files, copy them to an external hard drive as a backup. If you have used macOS Big Sur for some time and saved lots of data on your Mac, it is time-consuming to copy all data to your external hard drive.

In that case, you can back up your data on iCloud if there's enough storage space. Or, back up your data with Time Machine for restoring after rollback macOS update.

Notably, macOS reversion will also erase all the passwords you used in macOS Big Sur, like passwords for apps and networks.

To save your passwords, you can check Keychain in iCloud when using it to back up data. Or write down all the accounts and corresponding passwords.

How to downgrade macOS Big Sur to Catalina

After the backup work is finished, it's time to erase the startup volume to make room for macOS Catalina.

Erase your Mac before downgrading macOS

The startup volume erasure task should be taken in macOS Recovery mode.

How to Fix Mac Recovery Mode Not Working

  • Restart your Mac and press and hold the Command + Option + Shift + R keys until you see the Apple logo or the spinning globe.
  • Select Disk Utility. Then, right-click the macOS-Data volume and click Delete APFS Volume.
  • Choose the macOS volume and click Erase.
  • Erase your startup volume
  • Set a name, choose APFS in the Format: box. Then, click Erase.

The erasing process will take a while, don't do any other operation during the process, or the startup disk may be damaged.

Downgrade to macOS Catalina via Time Machine Backup

After the startup disk being erased, choose Disk Utility > Quit Disk Utility to return to the macOS Utilities window.

The macOS downgrade becomes very easy as you have a Time Machine backup that includes macOS Catalina.

  • Connect your Time Machine backup drive containing macOS Catalina to your Mac.
  • Select Restore From Time Machine Backup in macOS Utilities window and click Continue.
  • Select the backup disk and click Continue.
  • Select the backup disk containing macOS Catalina
  • Choose the destination (typically your Mac's internal hard drive) to save your Time Machine backup.
  • Click Restore to retrieve the Time Machine backup (including macOS Catalina and your personal data).

The restoring process will take some time. You can watch TV till the process done. Then, your Mac will restart automatically and run macOS Catalina.

How to fix Time Machine restoring failure

Downgrade to macOS Catalina in macOS Recovery mode

However, if without a Time Machine backup which includes macOS Catalina, what should you do?

If your Mac initially shipped with macOS Catalina ( Mac models released in late 2019 to 2020), you can roll back macOS update with the Reinstall macOS utility in Mac Recovery mode.

Make sure that your Mac is connected to the network in Mac Recovery mode.

  • Restart your Mac while holding Shift + Option + Command + R keys.
  • Release the keys until seeing the spinning globe.
  • Select Reinstall macOS in the macOS Utilities window.
  • Follow the instructions to reinstall macOS Catalina.

For the Mac shipped with macOS Mojave or earlier, you can downgrade macOS Big Sur to the initial version in macOS Recovery mode first, and then upgrade it to macOS Catalina in App Store.

Downgrade macOS Big Sur with a macOS Catalina bootable installer

If you have some trouble with the above two ways, you can try to downgrade macOS Big Sur via creating a macOS Catalina bootable installer.

As a Mac with an Apple T2 security chip doesn't allow starting up from an external drive by default, you should alter the security setting before creating the bootable installer.

  • Check if your Mac with Apple T2 chip in Apple menu > About This Mac.
  • If it has, boot into macOS Recovery mode.
  • Select Utilities > Startup Security Utility.
  • Check Allow booting from external media.

Then, restart your Mac, and go ahead to create a bootable installer.

Note: If you had erased your Mac when trying the two ways to downgrade macOS Big Sur mentioned above, you need to create the bootable installer on another healthy Mac.

  • Prepare an external hard drive with no less than 12GB in size.
  • Erase the external hard drive to APFS in Disk Utility (If it is, skip this step).
  • Download macOS Catalina installation files from App store. (Don't allow the install process starting at this time).

Note: The macOS download process will take a while. During the process, confirm that your monitor is on, the internet is connected, and the Mac is charged.

  • Connect your APFS formatted external drive to your Mac.
  • Open Finder > Applications > Utilities > Terminal.
  • Enter the following command and press Return. Here "MyVolume" in the command means where the macOS installation files will be stored, replace "MyVolume" to the name of your external hard drive.
  • sudo /Applications/Install\ macOS\ --volume /Volumes/MyVolume
  • Type your admin password when asked and press Return.
  • Enter Y when warning you that it will erase the external hard drive and press Return.
  • Wait until see the "Copy complete and Done" notification.

Now, you have created a macOS Catalina bootable installer.

Please confirm the internet connection is okay. Then, using the bootable installer to reinstall macOS Catalina on your Mac.

  • Restart your Mac while holding the Option key until seeing the list of startup disk options.
  • Choose the startup disk with macOS Catalina installer and click Restart.

Select the startup disk with macOS Catalina installer

Then, waiting for your Mac reboot from macOS Catalina.

Restore your data after downgrading to macOS Catalina

After the macOS Big Sur downgrade to macOS Catalina, the last step is restoring data from the backup you've maken just now.

If you saved the necessary files or folders on an external hard drive, move them to your Mac. Or, if you have backed up your Mac with Time Machine, you can restore the data you want with Migration Assistant.

Take care that don't restore the macOS Big Sur files, which will make your Mac back to macOS Big Sur.

Nevertheless, if your Time Machine backup lost or not working, you can get help from iBoysoft Data Recovery for Mac, which has free trial and focuses on recovering lost files, documents, folders, and etc.

As we know, downgrade macOS is not an easy task and will cause data loss. However, this post offers a complete guide of downgrading macOS Big Sur in steps, enabling you have the bigest chance to go back to macOS Catalina successfully.

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